Effects of wet treatment on bonding strength and electrothermal performance of electrothermal plywood bonded with emulsion polymer‐isocyanate adhesive

Abstract To create a green, safe, and aldehyde‐free indoor heating environment, an eco‐friendly emulsion polymer‐isocyanate (EPI) adhesive was applied to the preparation of electrothermal plywood with built‐in carbon fiber paper. The optimized process parameters of electrothermal plywood were 0.9 MPa, 120°C, 6 min, and 200 g/m² for hot‐pressing pressure, temperature, time, and glue spread amount, respectively. After water immersion for 24 h, the bonding strength of wet‐treated electrothermal plywood decreased to 0.89 MPa. The pull‐out cracks of the carbon fiber paper were the main fracture form of the wet‐treated electrothermal plywood, and the wood failure percentage was 0%–10% under the tensile load. Hydrolysis of the adhesive layer of the wet‐treated electrothermal plywood occurred. The relative C and N contents in the wet‐treated electrothermal plywood decreased by 6.1% and 25.3%, respectively. Moreover, the resistance of the wet‐treated electrothermal plywood increased by 273.4% because the internal conductive path was interrupted during the intrusion of the water molecules. The highest electric‐to‐radiant transfer efficiency of the electrothermal plywood was 72.4%, with a power density of 200 W/m². In conclusion, wet treatment has a significant effect on the bonding strength and electrothermal performance of the electrothermal plywood bonded with EPI adhesive.